Visible light communication transmitter and visible light communication system

Abstract

Visible light data communication with a sufficient transmission speed is performed using a general-purpose and cost-advantageous blue-light-excitation-type white LED without using a blue color filter while preventing the element from being damaged. When transmission data is inputted to a driving waveform generation unit ( 110 ) in a transmitter ( 100 ), the driving waveform generation unit ( 110 ) and a multi-gray scale driving unit ( 120 ) generate a multi-gray scale driving signal, which is supplied to the blue-light-excitation-type white LED ( 140 ) and allows the blue-light-excitation-type white LED ( 140 ) to emit light. A light signal outputted from the blue-light-excitation-type white LED ( 140 ) is collected by a lens or the like, is made incident into a PD ( 210 ) in a receiver ( 200 ), and is converted to a current signal. The current signal is converted into a voltage signal in a trans-impedance amplifier ( 212 ). Further, the light signal is subjected to equalization processing in an equalizer ( 214 ) and then is digitized by a limiting amplifier ( 216 ), thereby obtaining output data.

The invention claimed is: 
     
       1. A visible light communication transmitter that drives a blue-light-excitation-type white LED based on a driving current signal generated in accordance with transmission data and outputs a visible light signal to a receiver, comprising:
 a multi-level driving unit that generates a multi-level driving current signal by adding a rising pulse when the transmission data rises and adding a falling pulse when the transmission data falls, 
 wherein a pulse width of the rising pulse and the falling pulse is ½ of a minimum pulse width of the transmission data. 
 
     
     
       2. A visible light communication system, comprising:
 the visible light communication transmitter according to  claim 1 ; and 
 a visible light communication receiver that receives the visible light signal output from the visible light communication transmitter, converts the received optical signal into an electric signal, and outputs received data. 
 
     
     
       3. A visible light communication system, comprising:
 a visible light communication transmitter that drives a blue-light-excitation-type white LED based on a driving current signal generated in accordance with transmission data and outputs a visible light signal to a receiver, said visible light communication transmitter including a multi-level driving unit that generates a multi-level driving current signal by adding a rising pulse when the transmission data rises and adding a falling pulse when the transmission data falls; and 
 a visible light communication receiver that receives the visible light signal output from the visible light communication transmitter, converts the received optical signal into an electric signal, and outputs received data, 
 wherein a driving current value corresponding to the transmission data is equal to or smaller than ⅓ of a current value of at least one of the rising pulse and the falling pulse. 
 
     
     
       4. A visible light communication system, comprising:
 a visible light communication transmitter that drives a blue-light-excitation-type white LED based on a driving current signal generated in accordance with transmission data and outputs a visible light signal to a receiver, said visible light communication transmitter including a multi-level driving unit that generates a multi-level driving current signal by adding a rising pulse when the transmission data rises and adding a falling pulse when the transmission data falls; and 
 a visible light communication receiver that receives the visible light signal output from the visible light communication transmitter through a color filter that removes at least a portion of light output from a phosphor of the blue-light-excitation-type white LED, converts the received optical signal into an electric signal, and outputs received data, 
 wherein a driving current value corresponding to the transmission data is equal to or smaller than 5/4 of a current value of the rising pulse and the falling pulse. 
 
     
     
       5. The visible light communication system according to any one of  claims 2 ,  3 , or  4 , wherein a modulation encoder is installed in the visible light communication transmitter, and a modulation decoder that decodes a modulation code modulated in the modulation encoder is installed in the visible light communication receiver. 
     
     
       6. A visible light communication system, comprising:
 a visible light communication transmitter that drives a blue-light-excitation-type white LED based on a driving current signal generated in accordance with transmission data and outputs a visible light signal to a receiver, said visible light communication transmitter including a multi-level driving unit that generates a multi-level driving current signal by adding a rising pulse when the transmission data rises and adding a falling pulse when the transmission data falls; and 
 a visible light communication receiver that receives the visible light signal output from the visible light communication transmitter, converts the received optical signal into an electric signal, and outputs received data, 
 wherein a modulation encoder is installed in the visible light communication transmitter, and a modulation decoder that decodes a modulation code modulated in the modulation encoder is installed in the visible light communication receiver, and 
 wherein a run length limited code, which is DC free, of which an encoding rate is ⅔, and of which a minimum run is 1, is used as the modulation code, and NRZI modulation is performed.